Rigify horse armature: hind leg bones seem wrong; tweak also on wrong layer?
I havent used the Rigify animal rigs but there are a few things I can share. Keep in mind that Rigify is tricky to customize. If there are too much edits it will not work right.

After adding bones in edit mode you have to let the rig know there are more bones in the chain. On the metarig go to Pose Mode and click on the Thigh bone. Now go to the Bone Properties panel on your right and find Rigify type> Limb Segments. Experiment with adding numbers here and generating the rig until you find it works.

In that panel you can also click on the layer where you want the tweak bones.